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A lot of things changed since #Kotlin 1.1, for example starting with Kotlin 1.5 the compiler is optimizing for loops of any combination of functions creating an integer progression. Check out the very unreasonable example near the end of this revised post: dev.to/cbeyls/explo...

The overhead of companion objects is worse than it seems when you drop down to the arm assembly. When accessing non constants, having to access the insurance means doing an initialization check at each call site.

You mean when accessing fields of Companion objects from the main class? I assume there is still some overhead yes but I didn't investigate. I also assume R8 improves things on Android by using staticization.